1. Field of the Invention
The invention relates to:
(1) a method of parting rubber from a surface and certain products formed from this process; and
(2) a method of making a synthetic blood vessel using a parting agent.
2. The Problems Associated with Known Ballon Catheters and Their Production Methods
Ballon-type catheters have numerous medical applications. They can be used for drainage (e.g. urethral, Foley, colostomy, ileostomy and septostomy catheters), as diagnostic aids (e.g. thermodilution catheters), for therapeutic purposes (e.g. embelectomy, transluminal angioplasty, endotracheal, tracheostomy, esophageal, and intra-aortic catheters), and in a wide variety of other medical applications.
To date, many of the known methods of making balloon catheters have had serious deficiencies. For example, most methods were complex, required repeated attempts to achieve successful practice, and, as a consequence, were costly. Additionally, and more importantly, virtually all the known processes produce a seriously deficient product. For example, the methods disclosed in U.S. Pat. Nos. 3,292,627, 3,304,353 and 3,452,756 all produce a catheter with a thermoplastic and/or polyurethane balloon layer. Thermosplastic balloons, following inflation, do not revert to their original shape and size. Furthermore, polyurethane balloons are unsuitable for certain in vivo uses as urine hydrolyzes polyurethane.
U.S. Pat. No. 3,983,879 discloses a method for making a silicone rubber balloon-type catheter. In this patent it is stated that silicone is more compatible with body tissues than the thermoplastic materials of the '627, '353 and '756 patents. In the '879 patent process, tape is first wrapped around the inflation hole, the inflation hole being the hole which leads to the catheter's inflation lumen. The tape serves to prevent adherence of the balloon layer to the catheter tubing when the tubing is dipped in a solution of the material which forms the balloon layer. Following the formation of the balloon layer, the hole is re-opened with a hot probe.
This process, in addition to being complex, costly, requiring precision labor, and being subject to error--particularly at the stage where the probe is used to re-open the inflation hole--produces a deficient product because:
(a) the tape forms annular shoulders at the respective ends of the wrappings; this can cause patient irritation as well as difficult catheter withdrawal and insertion during in vivo catheter use;
(b) re-opening of the hole with the hot probe can result in a weak spot in the balloon layer as the probe must be passed through the balloon layer;
(c) the tape is wrapped around the tubing in an overlapping fashion thereby forming an irregular surface and resulting in an irregular balloon layer;
(d) it is difficult to re-open the hole as it is hidden from view by the tape wrapping;
(e) melting the tape can result in fragmentation of the tape--should the balloon break during in vivo catheter use, tape fragments can enter the body;
(f) tape fragmentation could also cause tape fragments to enter the balloon inflation hole thereby preventing in vivo balloon deflation and making catheter withdrawal difficult.
Thus, what is needed is a process for making balloon catheters which is easy to practice, inexpensive, and produces a balloon catheter without the deficiencies of the known products. The catheter should be made of a bio-compatible material which is not hydrolyzed by body fluids. The balloon layer should be made of a material which reverts to its original shape following inflation; there should be no ostensible ridges or surface irregularities in the balloon layer vicinity. Furthermore, there should be no ostensible weak spots in the balloon layer and no non-compatible materials within the balloon layer.